Study On Chemical Depolymerization Of Polycarbonate Materials In Deep Eutectic Solvents

Polycarbonate(PC)is an important engineering plastic and widely used in the manufacture of compact disks,glass assembly industry,automotive industry,medical devices and food packaging.With such a tremendous consumption,a large number of waste PC has caused serious environment pollution and resource waste.Therefore,the recycling of waste PC materials has become one of the most important issues to be resolved.In this paper,we describe the use of three different types of deep eutectic solvents(DESs)as catalysts for methanolysis reaction of waste PC under milder reaction conditions,which could effectively realize the utilization of waste PC materials as resource and provides a theoretical foundation for its efficient recycling.Choline chlorides(Ch Cl)was used as a hydrogen bond receptor in composition with some amides,carboxylic acids,hydrated metal chlorides which used as hydrogen bond donors to synthesis a series of choline chloride-based DESs for catalyzing the methanolysis of PC.The most effective DES was found as Ch Cl-2urea formed by Ch Cl and urea with the molar ratio of 1:2,and obtained the optimum reaction conditions: reaction temperature was 130 °C,reaction time was 2.5 h,m(Ch Cl-2urea): m(PC)=0.1:1,n(methanol): n(PC)=5:1,the conversion of PC could reach 100% and the yield of BPA could reach 99.8% under the optimized conditions.The structure of Ch Cl-2urea was characterized by FT-IR and 1H NMR,and it was proved that Ch Cl and urea were combined by hydrogen bonding to form Ch Cl-2urea.The structure of the product was characterized by FT-IR and 1H NMR,and it was confirmed that the product was bisphenol A.The reuse performance of Ch Cl-2urea in methanolysis of PC was investigated,Ch Cl-2urea could reuse 5 times with no apparent decrease for the conversion of PC and the yield of BPA.The kinetics of methanolysis of PC catalyzed by Ch Cl-2urea was further investigated,the result indicated that this reaction was a first-order reaction with a reaction activation energy of 141.47 k J/mol,and the possible mechanism of methanolysis of PC was proposed.The structure optimization of Ch Cl,urea and Ch Cl-2urea was carried out by means of density functional theory,and the energy barrier of the methanolysis of PC catalyzed by Ch Cl-2urea was calculated.It was found that the hydrogen bonding of Ch Cl-2urea with methanol was contributed to the forward of methanolysis of PC.In order to obtain DESs with lower viscosity,lower melting point,wider liquid range and better thermal stability,1-methyl-3-hydroxyethyl imidazole chloride salt([EMIMOH]Cl)was used as a hydrogen bond receptor in composition with some amides,carboxylic acids,polyol,hydrated metal chlorides which used as hydrogen bond donors to synthesis a series of N-methylimidazole-based DESs for catalyzing the methanolysis of PC.The most effective DES was found as [EMIMOH]Cl-2urea formed by [EMIMOH]Cl and urea with the molar ratio of 1:2,and obtained the optimum reaction conditions: reaction temperature was 120 °C,reaction time was 2 h,m([EMIMOH]Cl-2urea): m(PC)= 0.1:1,n(methanol): n(PC)= 5:1,the conversion of PC could reach 99.8% and the yield of BPA could reach 98.9% under the optimized conditions.The structure of [EMIMOH]Cl-2urea was characterized by FT-IR and 1H NMR,and it was validated that [EMIMOH]Cl and urea were combined by hydrogen bonding to form [EMIMOH]Cl-2urea.The structure of the product was characterized by FT-IR and 1H NMR,and it was confirmed that the product was bisphenol A.The reuse performance of [EMIMOH]Cl-2urea in methanolysis of PC was investigated,[EMIMOH]Cl-2urea could reuse 4 times with no apparent decrease for the conversion of PC and the yield of BPA.The kinetics of methanolysis of PC catalyzed by [EMIMOH]Cl-2urea was further investigated,the result indicated that this reaction was a first-order reaction with a reaction activation energy of 133.52 k J/mol,and the possible mechanism of methanolysis of PC catalyzed by [EMIMOH]Cl-2urea was proposed.It was found that alkaline DESs has good catalytic activity for methanolysis of PC.To take a step further research,Tetramethyl hydrazine(TMG),1,5-diazabicyclo[4.3.0]non-5-ene(DBN),1,8-diazabicyclo[5.4.0]undec-7-ene(DBU)and triethylenediamine(TEDA)were used as hydrogen bond receptors in composition with urea,triethanolamine,benzyl alcohol which used as hydrogen bond donors to synthesis a series of strong base-based DESs for catalyzing the methanolysis of PC.The most effective DES was found as DBN-urea formed by DBN and urea with the molar ratio of 1:1,and obtained the optimum reaction conditions: reaction temperature was 70 °C,reaction time was 2 h,m(DBN-urea): m(PC)= 0.05:1,n(methanol): n(PC)= 5:1,the conversion of PC could reach 99.4% and the yield of BPA could reach 96.5% under the optimized conditions.The structure of DBN-urea was characterized by FT-IR and 1H NMR,and it was proved that DBN and urea were combined by hydrogen bonding to form DBN-urea.The structure of the product was characterized by FT-IR and 1H NMR,and it was confirmed that the product was bisphenol A.The kinetics of methanolysis of PC catalyzed by DBN-urea was further investigated,the result indicated that this reaction was a first-order reaction with a reaction activation energy of 43.02 k J/mol.In summary,Ch Cl,[EMIMOH]Cl,DBN and urea were all combined by hydrogen bonding to form DESs.It was found that Ch Cl-2urea,[EMIMOH]Cl-2urea and DBN-urea have good catalytic activity on methanolysis of PC.It was found that with increase of basicity of DESs,The catalytic activity would be higher,reaction temperature and activation energy would be lower,and the reaction would be easier to carry out.The result also showed that the catalytic activity of DBN-urea was higher than [EMIMOH]Cl-2urea,and the catalytic activity of [EMIMOH]Cl-2urea was higher than Ch Cl-2urea.As far as we know,the above fundamental studies have not been reported in the literature.